This invention generally relates to electro-plating or electro-coating of components. In particular, the invention relates to means for masking areas on components to be plated or coated.
In the plating and coating industries, unpainted metal components are hung on metal racks for conducting electricity to the components during painting or coating. In the case of coating operations, the metal rack is moved to a position overlying a tank filled with water-based painting or coating solution. In the case of plating operations, the tank is filled with electrolyte solution. The suspended components are immersed in the solution by lowering the metal rack using conventional equipment. When a dc voltage is applied across the metal rack and the tank, the components on the rack become electrified, with the fluid being positive and the components being negative. As a result of the applied voltage, an electrical current is produced through the solution and components. For coating operations, this electrical current activates the organics of the paint or coating material and makes that material xe2x80x9cdrawxe2x80x9d to the unpainted surface areas of the components. As the plating material xe2x80x9cdrawsxe2x80x9d, it coats the component. For plating operations, metal or alloy is electrolytically deposited on the immersed component surfaces.
The only surface areas not coated with paint or plated with metal during coating or plating will be those submerged areas of the component where a mask has been applied. One known type of masking material is tape designed to withstand the high temperatures which occur in a coating or plating bath. The masked surface areas will not be coated or plated because the mask blocks contact of the liquid coating or plating solution with those surface areas of the component.
In the electro-coating and electro-plating industries, many different styles of expensive masking have been developed and used. The particular masking used depends on the particular plating or coating operation. For example, in two-cycle internal combustion engines, it is known to plate the side faces of the connecting rods at their crank ends with silver. This silver plating will then bear the frictional rubbing contact with the crank faces of the crank arms or disks of the crankshaft.
One known method for applying silver plating to the side faces of the crank end of a connecting rod involves the following steps. First, the connecting rod is subjected to electro-coating, i.e., electrodeposition painting. In electrodeposition painting, paint is suspended in water in particulate form and then charged with either positive or negative electricity. Connecting rods are immersed into the fluid and then charged with the opposite polarity of electricity. This will then excite the paint and draw it to the unpainted areas of the connecting rod and cause the paint to xe2x80x9ccoatxe2x80x9d the connecting rod to a specified thickness according to the time and amperage applied to the components/paint. The connecting rods then baked to xe2x80x9ccurexe2x80x9d the paint and make it extremely hard. The paint acts like an insulator to prevent the silver from adhering to exposed metal surfaces. After painting, the metal surfaces on the connecting rod which need to be silver plated are xe2x80x9creexposedxe2x80x9d by running the connecting rod through a grinder. Both ends of the connecting rod have the same thickness and when the rod goes through the grinder, the grinder exposes not only the large end faces of the crank end of the connecting rod but also the small end faces of the piston end of the rod which is coupled to a wrist pin. When the connecting rod is plated after the grinding operation, the painted surfaces will not be plated while all re-exposed metal surfaces will be plated. This is undesirable, however, because the presence of silver plating on the small wrist pin end of the connecting rod serves no purpose. It also costs extra money by using additional silver metal, which is expensive.
Thus, in the specific situation just described, and other situations, there is a need for a method of silver plating which would allow the component manufacturer to apply silver to less than all of the exposed metal surfaces of the component. More generally, when plating or coating is done in narrow deep tanks, the quantity of components being plated/coated must be maximized by totally immersing successive rows of components. In the case of a narrow deep tank, the surface of the plating or coating solution has insufficient area to allow productive plating or coating by immersing the components only partially. The depths of a deep tank must also be efficiently utilized. In systems having narrow deep tanks, there is a need for a technique and for equipment which would allow only certain portions of fully immersed components to be plated or coated. In particular, there is need for an alternative to the use of expensive masking tape that is not re-usable, which masking technique adds permanent costs without added value to the components to be plated.
The present invention is directed to a method and an apparatus for restricting the areas of contact between components to be plated or coated and liquid solutions containing plating or coating agents, without the use of masking tape. In accordance with the preferred embodiments of the invention, components are suspended underneath a concave structure, with portions of the components that should not be plated (or coated) being disposed within the interior volume defined by the concave structure. Then the suspended components and the concave structure are fully immersed in a bath of plating (or coating) solution. The concave structure is disposed so that air is trapped under it when the structure is immersed in the liquid solution. The resulting air pocket surrounds the portions of the components which are not to be plated (or coated), prevents the liquid solution in the bath from entering the interior volume of the concave structure and touching those portions. In other words, the air acts as a xe2x80x9cblindxe2x80x9d or mask that prevents paint or metal from contacting or adhering to surfaces not to be plated (or coated).
A method of coating or plating in accordance with one preferred embodiment of the invention comprises the steps of: placing a component made of electrically conductive material in a position relative to a concave structure such that a portion of the component protrudes inside the concave structure; immersing the component and the concave structure in a solution containing plating or coating material so that an air pocket is formed beneath the concave structure; and plating or coating only the portion of the component which protrudes outside the concave structure.
A system for plating or coating in accordance with another preferred embodiment comprises: a rack; an electrically conductive mounting supported by the rack; an electrically conductive component coupled to and in contact with the mounting; a concave structure supported by the rack, the concave structure being configured and positioned so that one portion of the component protrudes outside and another portion of the component protrudes inside the concave structure; and a tank holding a solution containing plating or coating material. The component and the concave structure are immersed in the solution with an air pocket trapped beneath the concave structure. Only the exposed surfaces of the component lying outside the concave structure are plated or coated.
A further aspect of the invention is directed to a method of masking a portion of a component to be plated or coated by covering that portion of the component with a buffer or pocket of air.
In accordance with the preferred embodiment of the invention, the concave structure referred to above takes the form of a bell housing having one end attached to a rack. In most cases the fluid buffer under the bell housing will comprise ambient air. However, the invention does not require the use of air. For example, in some situations, it may be preferable to fill the space under the bell housing with inert gas.
The invention has application in electro-plating or electro-coating any components which can be suspended under a concave hood or bell housing or similar concave structure. The hood or bell housing can be specifically designed to meet the needs of a particular application. The hood or bell housing must have an interior volume sized and shaped to receive the portions of a multiplicity of components which are not to be plated or coated. Multiple hoods or bell housings can be mounted on a circulating rack system which immerses multiple rows of components in the plating or coating bath at the same time.
This application is extremely unique as most masking agents or materials are required to be applied singly to each part and require some manual application and removal. With this type of housing, the parts can be loaded as fast as if there were no housing at all. In addition, the masking requirements can be completely bypassed. This saves the cost of the masking and the time involved with the application/removal of the masks.